Traveling-wave tube attenuators



June 7, 1960 K. E. zUBLIN EVAL 2,939,993

TRAvELING-WAVE TUBE ATTENUATORS Filed Jan. 7, i957 5 Sheets-Sheet l FIC-3.4.

INVENTORS: KURT E. ZUBLIN, ROBERT A. CRAIG,

l THEIR ATToRN Y.

June 7, 1960 K. E. ZUBLIN EVAL TRAvELmG-WAVE TUBE ATTENuAToRs Filed Jan. i, 1957 3 Sheets-Sheet 2 mm IY KLA R RER/ 0 UC T 0 Z 4 MEA E T IR VTR l NRE F. -mw m June 7, 1960 K. E. zuBLlN ETAL 2,939,993

TRAvELING-WAVE: TUBE: ATTENUATORS Filed Jan. '7, 3.957 3 Sheets-Sheet 3 l n l n l INVENTORSI KURT E. ZUBLIN, ROBERT A. CRAIG THE ATTO EY.

United States Patent O 'RAVELlNG-WAVE TUBE ATTENUATORS Kurt E. Zublin, Menlo Park, and Robert Craig, Palo Alto, Calif., assignors to General Electric Company, a corporation of New York Filed Jan. 7, 1957, Ser. No. 632,341

13 Claims. (Cl. S15-#3.5)

This invention relates to electron discharge devices and vmore particularly to improvements in high frequency electron discharge devices of the traveling-wave tube type.

Traveling-wave tubes may be employed in various applications and appear to be particularly suitable as amplitiers for high-frequency operation over a wide bandwidth. Some traveling-wave tubes employed as amplifiers include a translating element in elongated form adapted for propagating an electromagnetic wave therethrough. The translating elements are adapted by construction and arrangement to decrease the velocity of the electromagnetic wave along the axis of the translating element to a magnitude substantially less than the velocity of the waves in free space. rl'he axial velocity of the electromagnetic wave is thus decreased to a velocity within the range of conveniently obtainable electron beam velocities. Such translating elements adapted for decreasing the axial velocity of an electromagnetic wave have been termed slow-wave structures. In the aforementioned amplifiers, input means may be provided for applying electromagnetic energy to one end of the slow-wave structure. Means may also be included for providing and directing an electron beam, which beam has a velocity approximately the axial velocity of the electromagnetic wave, and in energy-coupling relation with the slow-wave structure. Means may also be provided at the other end of the slow-wave structure for coupling out the amplified electromagnetic wave.

In such traveling-wave tube amplifiers, the useful gain which may be secured may be limited by unwanted reections of electromagnetic waves by impedance mismatches between the slow-wave structure and the input or output coupler. The harmful effect of such mismatches, which heretofore have been unavoidable, are minimized, according to one feature of our invention, by incorporating in the slow-Wave structure one or more attenuating sections which provide a very good electromagnetic match thereto. Such attenuators largely absorb rather than transmit 'or reect the incident electromagnetic waves and therefore prevent successive energy reections-which degrade the performance of the amplifier and may in extreme cases lead to unwanted oscillation.

It is accordingly a principal object of the present invention to provide a traveling-wave tube adapted for high power level operation.

It is another object of the present invention to provide a novel attenuator device for use in connection with a slow-wave structure that is conducive to maintaining high eiciency of operation.

It is another object of the present invention to provide such a device in which the energy loss material is capable of dissipating relatively large amounts of heat, thereby providing short-circuited stable operation of the travelingwave tube.

It is another object of the present invention to provide such a device in which the energy-loss material is concentrated in a relatively short length of a slow-wave It is another object of the present invention to provide such a device in which the energy-loss material or its resistivity may be tapered in a radial rather than axial direction.

It is another object of the present invention to provide such a device in which the performance is relatively insensitive to the resistivity or dimensions of the energy-loss material.

Further objects and advantages will become apparent from the following description and the features of novelty which characterize the invention will 4be pointed out with particularity in the claims annexed to and forming part of the invention.

In the attainment of the foregoing objects, we provide traveling-wave tubes including slow-wave structures consisting of periodic sections in seriatim. Attenuation members consisting of a relatively high-loss material concentrated in a relatively short length and having a crosssectional area approximately equal to the area of crosssection of the slow-wave structure are disposed in the slowwave structures; one or more of said attenuation members interposed between predetermined ones of said periodic sections.

For a detailed explanation of our invention, reference is made to the accompanying drawings in which like reference characters designate like elements throughout and in which:

Figure l is an axial cross-sectional View of a travelingwave tube in accordance With the invention;

Figure 2 is an enlarged exploded view in perspective of the attenuator assembly of Figure l;

Figure 3 is an enlarged axial cross-sectional view of the assembled attenuator of Figures 1 and 2;

Figure 4 is an axial cross-sectional View of another embodiment of the present invention;

Figure 5 is a fragmentary cross-sectional view of a portion of yet another embodiment of the present invention;

Figure 6 is an exploded view of another embodiment of attenuator assembly according to the present invention; and

Figure 7 is a longitudinal cross-sectional view of the assembled attenuator of Figure 6.

In Figure l there is illustrated a traveling-wave tube 11 in accordance with one embodiment of the present invention. Tube 11 includes an electron gun 15 consisting of a cathode 19; a cathode heater 21 connected to a suitable energizing source (not shown); va centrally apertured electron beam focusing electrode 23; and a centrally apertured electron beam accelerating anode 25. Electron gun 15 is located in a dielectric bulb 27 at one end of the tube 11, the left-hand end as oriented in the drawing, and provides an electron beam depicted by broken lines Y53 which may be directed along the axis of the tube 11 as will be detailed hereinbelow.l

An elongated slow-wave structure 29 is disposed between the electron gun 15 and a collector anode 31 located at the right-hand end of the tube li.. The slowwave structure 29 may be a waveguide consisting of a series of spaced transverse conductive bailie plates 43 suitably aixed to a tubular conductor 45, the plates producmg a structure in the nature of a loaded Iline to reduce the velocity of electromagnetic waves propagated therethrough to a value substantially below that in free space. Each of the plates 43 has a centrally located aperture Lio for permitting passage of the electron beam 53. An attenuator assembly 49, the details or" which will be described hereinbelow, is disposed approximately midway between the ends of slow-wave structure 29. Collector anode 31 may consist of a capped tubular metallic member having an open end which may be joined to an output waveguide 51, and thence to the light-hand may be directed through i Y Y y y Y and'in a path along the axis of the slow-wave structure Ythe slow-wave structureV t K Av suitable attenuator dls end of: the slow-wave structure 29. The bulb member V27, Y Yslow-weave structure 29, waveguide SLand the collector 31 may be sealed in any suitable manner to provide Van air-tight Yvacuum envelope. The collector 31 dissipates residual energy of the electrons and mayv becooled, necessary, in l any suitable manner as,` for Iexamplepby conduits 54 adapted to convey a cooling medium |there#l through. j l

. The electron beam 53 ofV predetermined `desired velocity i the apertures 'w46 of plates 43 29. FocusingV of the beam Vvf3'tliroughout its travel along 249 axis may be obtainedmby amagneticV field directed along the axis Vof the structure 29. A solenoid 55 for producing such a teldjsurrounds the ttibe 11 Yalong its length in order top maintain a sub-V stantially constant axial'fieldcomponentY To simplify the drawing, theI connection of the solenoid to a current source is not shown. .i n A v Y v i n electromagnetiowave may be corupledwto the lefthand or cathode end of thevslow-wave structure'29 Vby yany suitable meansrknown in -the art andas shown, for example, by a coaxial line'57/ having inner conductor 59 connected to the slowfwave structure 29 in such' a way as torform either probe or loop coupling to the first sec- Y 5 tion'thereof, and outer conductor 61 connected to ground reference. e Output coupling means `consisting of any type known in the-art suitablefor high-.power level operatlon suchras, foreexample', the waveguide structure 51Y having a coupling probe V65 inserted `in the broadrwall of the waveguide is provided at the opposite or collector end of the slow-wave structure 29 to couple` the output from the traveling-wave Vtube 11i/to aV utilization circuit, not

Y. a more positive potential thanis' applied to cathode 19,

' As seen in Figures l, 2 and 3, attenuator assembly e? may include a pair of disks 71 and 73 which may be identical to one another and YformedV of lossy orenergyjdissipating material such as, for example, carbonized porous ceramics, lossy ferrites or any such lossy materials which have the property VthatY the amount of loss introduced thereby can'be controlledV Furthermore, the materialis desirablyy one which is relativelyrstable with temperature.V Y y Y We have found that materials ofA whichfthe'resistivity 'is of the order of one Vthousand times that of carbon give suitable loss and have the desirable property lthat'the Y waive-absorbing property is relatively insensitive 4tothe resistivity/or `tolerance dimensions of the energy-dissipatingbo'dy,4 Y d* y k construction that we have found to operate satisfactorily is fabricated from a disk ofV porous alumina that has been preliminarily soaked,

at roomV temperature, for a few'hours in an aqueous sugarV solution. The concentration of the' solution can range Y from approximately to V50% according to the de- Y sired resistivity.Y After drying in hot air at any convenient temperature belowtZOG degrees centigrade,V the body is thereafter tired for about l0 minutes in a neutral atmosphere at about 1000 degrees C. We have found that ring in a hydrogen furnace produces a desirable product. The dryness of the hydrogen is relatively important since a very small amount of oxygen is sucient to burn off carbon. The firing operation transforms the sugar intocarbon having the aforementioned desirable loss `cltlaracteristic that is relatively insensitive to resistiv- Y-Vity ortolerance dimensions of the attenuator body.

Disks 71l :and 73 are'l located at a predetermined point agencesl f along the length 4of the slow-wave structure 29 and de sirably near the center of the slow-wave structure. The cross-sectional area of disks 71 Yand 73'of the attenuator 49 is effectively equal to or corresponds to the cross- Asectional area of the slow-wave structurer29, although employment ofV bodies fabricated as above-described yields considerable freedom as to `dimensional tolerances.

V"llieiindividual elements ofv attenuator 49y are shown in the exploded view of Figure 2r. A centrally apertured circular conductive plate 75 'has an loutstanding Vilange or'drift tube 77 in the region of the central aperture and is disposed between the disks 71 and 73. Plate 75 includes ledges or rings 79 andgl Vlia-ying an Yinner diameter approximately equalto the outer diameter of the disks 71 and 73 to provide snug fit therefore. Plate 75v provides radio-frequency isolation between the input and output ends of the slow-wave structure 29. The plate 75 provides fthe additionalaction of cooling theqattenuator discs 'i1 and 73,. `'l`hisqcooli-ng action .is suflicient `for most applications; However, it has been found that the thiekf ness of therplvate 75V caribe varied without deleterious effects on tube performance, consequently, cooling ducts (not shown) may be provided inside this plate and 4:a cooling fluid Ycirculated therein'.Y With such an arrangement, the attenuatordiscs 71 and 73Qarre cooledfto ,a

' temperature dependent upon the radio'frequency power absorbed in the attenuator, the ratevr of fluid fiow, and the iluid temperature aswell as the.particulan-geometry of` the combination of plateV 75 and discs '771- and 73. When assembled, lthe driftrtube 77 extendsalongthe inner rim of the disks .71 Vand 73 and shields thedisks romjnipingemerrt Y,by the electron beam 53,.,l VTwoslotted metallic conducting ,couplingpiecesjd and vhave respective sets of raised Vledges Yor ringsn87, $2 and 97.1,A 93 Y to 'snugly receive and support' theVV disk members 71 and 73, respectively, CouplingpiecesS andSSvhave respective outer anges and 97 which` may beadapted to bear against rim 32 of plate 7 5.r Coupling pieces S3 and 85 provide additional Ysrarbo-frequency matching network necessaryY in some .cases ton eliminate reflections from the attenuatins disks- Y*T histvre Cpnstruction provides@ 'Compactassemblr which mayroccupy inl thetube apar@- irriatelyrthe same Vlongitlniinallength asy but one section ofthe slow-wavestructure 29.V 4 i .Y If desired, 9i" Where-required' to'improve. vntittr 0f Ytransition between themattenuator sections and the Ynext adjacent slow-wave section, thev lisks `71V andj ,may be actually 0rv effectively tapered `in a radial drectibn relative the axisof the( tube. V Y"Alf-bus, instead of being of uniformaxal thicknesses shown, the disks, may lbe of non-unionY thickness, as, fo; example, by having a maximum thickness Aat the peripheral region and a relatively finster thin Vinner @dse-f AISO, and depending Qn thervb- Servedmode Of' excitativa ofthe diacrentisections, the dSkSv'may be tapered with t1/ minimal thickness near the per-ipherxvalY edgeY and maximal thickness at the center. The ftaper can be employed with linear variation of thickness or other relations such as "L Y wherer is the Kradius of uthe, disk, according pto theV desite@ Smcgthness oteletric'al. contitmitvY ,sought to beac- ,Cvmplshed- It-Will'be understood that .in lieu( of geo,- metrical tapering as just describedhay tapering effectcan be awmrlished as'br selectively and radially *,cntrolling the density or amountY of lossy material embedded within uniform-thickness. ceraniic or other porous base.V

The slow-wave structure 29 consists of anrinput portion 42'separa'te, andV in axial' alignmentV with; amont- ]gzut portion44.Y In operation of tube 1,1, an electro- Amagnetic", 'wave is` coupled bycoax'i'al line; 57 tothe' input portioni42 of the's1ow-`wave' structure 29 and isv ropagated along the :slow-wave'A structure'29 Yand se' Vto modulate the electron beam 53 being directed through the slow-wave structure. The electromagnetic wave is completely absorbed, Vfor all practical purposes, in the lossy disk terminating member 71. The electron beam 53 which has been modulated by the input electromagnetic wave passes through the aperture 77 inV attenuator 49. The electron beam 53 generates high frequency energy in the output portion 44 of the slow-wave structure 29 in accordance with the input modulation. The amplitied output energy is coupled to the waveguide 51 -by the coupling probe 65.

Since the attenuator assembly 49 may be constructed to provide almost complete absorption or decoupling of the electromagnetic wave, the input and output portions of the traveling-Wave tube may vbe made to serve entirely diierent functions such as, for example, would be required #in a generator of harmonic components of the fundamental electromagnetic Wave introduced into the input end 42 of the slow-wave structure. In such a case, the output portion could be designed to amplify a harmonic of the frequency of the input portion. The input portion 42 may conceivably -be constructed as a tunable oscillator and the output portion may be adapted to amplify the oscillation frequency or a harmonic thereof.

Figure 4 shows a slow-wave structure 99 employed in a traveling-wave tube of a similar type to a slow-wave structure 29 of Figure l and in which a plurality of slowwave structure portions or stages, isolated electrically from one another by attenuators, provide high power gains while eliminating any tendency toward undesired oscillations. The slow-Wave structure 99 includes three operating stages 101, 103 and 105 which are isolated electrically from one another by attenuator assemblies 197 and 109, each of which attenuators may be similar `to attenuator assembly 49 of Figure l. An electron beam 53 is modulated by an electromagnetic wave coupled to the input portion 101 of slow-Wave structure 99 from an inputl coaxial line 57. An attenuator disk 111 on the input line side of the attenuator 107 absorbs the electromagnetic Wave, but allows the modulated beam to proceed to the next portion 103 where the beam energizes an augmented electromagnetic wave therein in accordance with the input modulation. An attenuator disk 113 on the output side of the attenuator 107 absorbs any reflected waves to prevent undesired oscillationsin that section of the tube. This operation of energizing an augmented wave is repeated in output portion 105, and as many times thereafter as desired to obtain the desired power gain in the amplier. The output energy may be coupled out through probe 65 inserted in a waveguide 51.

Another embodiment of the attenuator construction according to the present invention is shown in Figure 5. An attenuator 121 includes a single lossy disk 123 apertured to accommodate an electron beam 53 which attenuator is inserted in the slow-wave structure 29 to provide attenuation. The slow-wave structure 29 and electron beam 53 may be similar to that of Figure 1. Slotted baille plates 125 and 127 disposed on either side of the disk 123 may be constructed, each having an inner ring support ledge l129 and 131 and an outer ring support ledge 133 and 135, respectively, to provide support for the disk member 123. The attenuator =133 is substantially reectionless and can ybe made of such dimensions and material that a predetermined fraction of incident electromagnetic energy can be attenuated or absorbed thereby. Varying degrees of attenuation can be obtained with the embodiment of Figure 5 as compared to almost complete absorption of the input electromagnetic wave desired to be provided by the attenuator of Figures 1 4. In one type of operation of a travelingwave tube employing the attenuator as shown in Figure 5 and having other elements otherwise similar to those of Figure l, an electromagnetic Wave is coupled to one end, not shown, of the slow-wave structure 29 and Ytransmitted directly through the slow-wave structure. The introduced electromagnetic wave is in continuous energyk 'interacting relation with the electron beam 53 throughout the length of the slow-wave structure 29. The augmented electromagnetic wave is extracted from the opposite end, notshown, thereof. The attenuator 133 can be made with just suicient loss to prevent undesired oscillations such as those caused by amplication of 'the backward traveling-wave or those caused by reflections from the impedance mismatch.

Figures 6 and 7 show still another embodiment of an attenuator assembly 137 according to the present invention. An attenuator assembly includes two lossy disk members 139 and 14'1.which may be fabricated as abovedescribed in connection With disks 71 and 73. A centrally apertured ilat conductive plate 143 having an outstanding flange or drift tube 145 in the region'of the central aperture-is disposed between disks 139 and 141. Two radially slotted metallic side Vpieces 147 and 149, each having an outer rim llange 151 and 153, respectively,V enclose the attenuating disks 139 and 141. Each of the side pieces 147 and 149 include a plurality of wedge-shaped conductive members 155 extending'radially inwardly from the rim flanges 151 and 15B and are quadrantally disposed between-adjacent pairs of slots, as shown. 'I'he side pieces 147 and 149, the wedge-shaped metallic members 155 and the spaces 156 between the members 155 which separate the side pieces from the attenuating disks 139 and '141 cooperate to deiine an impedance matching network which we have found useful to eliminate rellections from the disks. A fuller description of the so-called clover-leaf structure of the aforedescribed type is given in a publication by one of us, Robert A. Craig, entitled, Study of Periodic Structures for High Voltage Traveling- Wave Tube Operation, Technical Report #36, dated November 2, 1954, and published by Stanford University. The attenuator assembly is shown as assembled in a portion of a slow-wave structure 157, Figure 7. Slow-wave structure 157 maybe of the clover-leaf structure.

As shown in Figure 7, the drift tube 145 may extend alongthe inner rim of the disks 139 and 141 to provide radio-frequency isolation between the input and output sections4 159 and 161 of the slow-Wave structure 157 as wellras partially to shield the disk from possible impingement by the electron beam. The length of the drift tube 145 may be selected to control the amount of decoupling between the two sections 159 and 161 and contributes in some cases to the impedance match. The operation of the just-described attenuator assembly in slow-wave structure 157 is generally similar to the operation of attenuator assembly 49 in slow-wave structure 29 described above in relation to Figure l.

While specific examples have been given describing details of this invention, it will be understood that they are lgiven merely by way of illustration and that the invention is to be construed as including other modiiications within the true spirit and scope of the appended claims.

What we claim as new and desire to obtain by`Letters Patent of the United States is:

l. An electron discharge device of the traveling-wave type comprising means for providing an electron beam, an elongated slow-wave structure, said slow-wave structure comprising a waveguide having a plurality of spaced transverse plates, each of said plates having a substantially centrally located aperture therethrough, input and output means connected at opposite ends of said slowvwave structure, an attenuation section interposed approximately at the center of s aid slow-wave structure, said attenuation section including a disk-shaped body of relatively high loss material having approximately the same cross-section as said transverse plates, and centrally apertured impedance matching means disposed on opposite sides of said body of high loss material, said attenuation section being positioned in substantial alignment with said transverse plates whereby'a continuous path is pro- V periodic sections.

ansa-cca 4vi'cled'through said plates and said attenuationsection to permit-passageof said 'electronb'eatn 1 Y Y :2. In an electron discharge device 'of the traveling-wave typea slow-wave structure comprising'a loaded waveguide, said waveguide comprisingga tbular member, a

Y plurality-,of extending spaced parallel transverseplates aixed to said tubular member, an attenuation section i Y disposed Yat a predetermined point in said slow-wavestructure,-said attenuation section comprising at least one atytenuation member and impedance matching means on opposite sides of said attenuation member, each said attenuation memberY being disk-shaped andihavin'g-approximatelythe Ysame cross-section as said slow-wave structure-.said'attenuation section and each of sai'd plates having a substantially centrally located aperture therethrough. V3. vIn an electron discharge device of the traveling-wave type, a slow-wave structure'comprising a plurality of periodic Vsections lcapable of propagating `an electromagnetic wave therethrough, -an attenuation sectionl in 'said slows-wave structure comprising a `first disk member, 1a second "disk member, :said disk members comprising lossy material and each having a cross-section `approximately the same as the cross-section of said slow-wavestructure, a first conductive plate interposedVV between and in contiguous relation with said disk members, said disk members disposed at a point alongV the length Vof said slowwave Vstructure to provide attenuation, and a 'pair of conductive plate members disposed on opposite sides 'of said disk-members adaptedto couple said wave to said disk member said nist andsecond disk'members, said conductive plate and said VVpair ofrconductive plate members' 7. lInv an "electron discharge device, V'a'slo,vv-wave structure comprising a yplurality, vof periodic sections :capable of'propagatin'g an electromagnetic wave therethrough, at least one attenuation `section of substantially the same cross-section as'said interacting portions for .terminating predetermined sections; of said slow-wave structure, at'

least Vvone disk member containing lossy material in each Y said attenuating section, and impedance matching means on opposite sides of said attenuationfsection for coupling electromagnetic Waves to said disk'member, said attenuation fsectionfhaving a centrally located aperture'therein to accommodate passage of an electron beam and being inserted in Vsaid, slow-wave Vstructure separating respective ones ofsaid periodic ise'c'tions, vthe-'said attenuation sections being'capable ofdis'sipating 'relatively large amounts Y ofelect'ror'n'ag'netic power for Vobtaining stable operation 1 In 'an electronV discharge device of of said wave 'structurel in `said device.

wave type Vhaving Aa Vslow-wave structure comprising a loaded waveguide,V said waveguideVY including an outer tubular member and a plurality ofl'in'wardly extending spaced parallel transverse plates, lsaid plates beingjoined each Ihavingrcentrally located yapertures the'rethroughforY accommodating the passageof an. elec't'ronfbeam'.VVV

'In an electrondischar-gedevice'ofthe Ytraveling-wave type,. a slow-wave structure comprising aY pluralityV of periodic 'sectionscapable of propagating fan electromagnetic wave therethrough, an vattenuation section in .said

slow-wave structure comprising a single diskV member',V

said plurality of Vperiodic sections and saidy attenuation section having Y,apertures therethrough to permitpassage of anelectron beam, said disk member comprisinga lossy material having la cross-section approximately the same fas thev cross-section of said slow-Wave structure, and. Ymeans including-'a pair. of conductiveplate members disposedon opposite sides of said disk members and adapted tofcouple said wave to saiddisk member. n

5. Inj anelectron discharge devicev off'a traveling-wave Y type having aV slow-Wavestructur'e in the form of a loaded waveguide having afplurality of periodic 'sections capable of propagating an electromagneticr wave therethrough, an

' Vattenuation section having substantially thesamecrosssection [as said periodic sections and comprising at least one disk member containinglossy material, and matching means ,on opposite sides ofsaid section for coupling said wave-.,tosaidjdisk member, said,V attenuation section havt 6.1. In; an: electron' discharge device, a slow-wave structure comprising a plurality of interacting portions in axial alignment ,and'rcapable ofpropagating an electromagneticV wave therethrough, attenuation/sections ofsubstantially the'rsame cross-section as lsaid interacting-portions for terminating respective vportions of-said slovsv/waveY struc- Yture, and-at least one of said attenuation sectitqmsinterposed between adjacent interactingportions,` the said' attenuation sections including at least one centrally aper- Yturled disk-shaped member of Vsubstanti'a'llythe same crosssection as said interacting portions and atleast a pair of centrally apertured impedance matching members dis-Y posed Von opposite sides Yor" Ysaid attenuation sections whereby said Vattenuation nsections are capable of dissipatin'gl'arge amounts of electromagnetic power for obtainingstable operation or said device in conjunction withV a-.wide varietyof loadV mismatches.

to `said tubular members 'and deiining `a Ycentral aperture for accommodating an Velect/ronY beam, an attenuation section adapted for insertion at a predetermined point Yin saidY slow-wave structure, said attenuation section comprising yat least one attenuation member having` a cross- 'sect'ion approximately equal to that of thefslow-fwave structure, said-attenuation member having an axial dimension comparable with that of one section of said slowwave structure, and support means `for said attenuation memb'en-said support means Ycomprisinga vpair of con-V ductive plates eachv having vradial* slots 'coupling Wave energy to said attenuation'member and Viiange means to support 'said v'attenuation member in predetermined VAfixed p'o'sitio'n'inV the tubular member'said'conductive plates and said 'attenuation member Yhaving centrally located aperr tures therethrough in substantial alignment'kwithj the said central aperture defined 'by said spaced parallel transverse plates to permit Vthe passage of the electron beam. r 9. An `electron discharge deviceof the traveling-wave type comprising a periodic slow-wave structure'cpableof propagating an electromagnetic wave therethrough, means Y producing an electron stream -i'n 'energy interacting relagated-'body porticn'of relatively low attenuation, at least Y one sectionof relatively high attenuation interposed at a "A VVing a centrally located aperture therethrough'disposedin said slow-Wave-structure between respective oncs'ofsaid tion'r with said Vslow-wave structure, means lcoupling electromagnetic wave energy to one end of said slow-wave structure, said slow-wave structure comprising anA elonpredetermined point along' thev length of saidv relatively low attenuation body portion, said high attenuation'section being ofappro'ximately the same cross-sectionalV area Y asfsaid body portion and including a centrally apertured 'disk-shaped! member of Ylossy materialV and centrally apertured impedance matchingV means on opposite sides fof said vdisk-shapednnember", the axial extension of said Ahigh attenuation section being in approximately the same order of magnitude as the spacing between periodicA portions of "said kslow-wave structures, and means coupled to the Vopposite end of said slow-wave structure for deriving energy therefrom. Y

v10. An 'electron discharge device-of the traverling-v'lave type comprising aV pen'odic'slow-wave structpre capable of propagating an electromagnetic wave therethrough,

the travelingof relatively high attenuation including impedance matching means for matching electromagnetic Waves propagating through the periodic slow-wave structure to said high attenuation section and means coupled to the opposite end of said slow-Wave structure for deriving energy therefrom.

1l. In an electron discharge device of a travelingwave type comprising a nearly periodic slow-wave structure through which an electromagnetic Wave is propagated, said slow-Wave structure comprising a plurality of sections of relatively 10W attenuation, and a section of relatively high attenuation interposed at a point along the length of said low attenuation section, said high attenuation section comprising a generally disk-Shaped material having substantially the same cross-section as the cross-section of said slow-wave structure and having loss properties or dimensions which are tapered in a radial direction to provide high attenuation for traveling electromagnetic waves, impedance matching means on opposite sides of said disk-shaped material, said high attenuation section having a centrally located aperture therethrough.

l2. In an electron discharge device of a traveling-Wave type comprising a nearly periodic slow-wave structure through which an electromagnetic wave is propagated,

said slow-Wave structure comprising sections of relatively low attenuation, a section of relatively high attenuation interposed at a point along the length of said low attenuation section, said section of relatively high attenuation having substantially the same cross-section as said low attenuation section and including a centrally apertured generally disk-shaped member of lossy material having substantially the same cross-section as said section of relatively high attenuation and centrally apertured impedance matching means on opposite sides of said diskshaped member, the performance of said high attenuation section being relatively insensitive to the loss properties or dimensions of the energy loss material.

13. In an electron discharge device of a traveling-wave type comprising a nearly periodic slow-Wave structure through which an electromagnetic wave is propagated, said slow-wave structure comprising sections of relatively low attenuation, a section of relatively high attenuation interposed at a point along the length of said low attenuation section, said section of relatively high attenuation including a material having a resistivity of the order of one thousand times that of carbon and a cross-section substantially the same as said section of relatively high attenuation and impedance matching means for matching said relatively high attenuation section to said low attenuation sloW-wave structure.

References Cited in the iile of this patent UNITED STATES PATENTS 2,122,538 Potter July 5, 1938 2,636,948 Pierce Apr. 28, 1953 2,644,930 Luhrs' July 7, 1953 2,712,614 Field July 5, 1955 2,760,161 Cutler Aug. 21, 1956 2,801,361 Pierce July 30, 1957 2,823,335 Dench et al Feb. 1l, 1958 FoRErGN PATENTS 660,660 Great Britain Nov. 7, 1951 

